Quantum Times: Physics, Philosophy, and Time in the Postwar United States The Harvard community has made this article openly available. Please share how this access benefits you. Your story matters Citation Crystal, Lisa. 2013. Quantum Times: Physics, Philosophy, and Time in the Postwar United States. Doctoral dissertation, Harvard University. Citable link http://nrs.harvard.edu/urn-3:HUL.InstRepos:11051191 Terms of Use This article was downloaded from Harvard University’s DASH repository, and is made available under the terms and conditions applicable to Other Posted Material, as set forth at http:// nrs.harvard.edu/urn-3:HUL.InstRepos:dash.current.terms-of- use#LAA Quantum Times: Physics, Philosophy, and Time in the Postwar United States A dissertation presented by Lisa Crystal to The Department of the History of Science In partial fulfillment of the requirements for the degree of Doctor of Philosophy in the subject of History of Science Harvard University Cambridge, Massachusetts April, 2013 © 2013 Lisa Crystal All Rights Reserved. Dissertation Advisor: Professor Peter Galison Lisa Crystal Quantum Times: Physics, Philosophy, and Time in the Postwar United States Abstract The concept of time in physics underwent significant changes in the decades following World War II. This dissertation considers several ways in which American physicists grappled with these changes, analyzing the extent to which philosophical methods and questions played a role in physicists’ engagement with time. Two lines of questioning run through the dissertation. The first asks about the professional identities of postwar American physicists in relation to philosophy, as exemplified by their engagement with the concept of time. The second analyzes the heterogeneous nature of time in physics, and the range of presuppositions and assumptions that have constituted this “fundamental” physical concept. The first chapter looks to the development of atomic clocks and atomic time standards from 1948-1958, and the ways in which new timekeeping technologies placed concepts such as “clock”, “second,” and “measure of time” in a state of flux. The second chapter looks to the experimental discovery of CP violation by particle physicists in the early 1960s, raising questions about nature of time understood as the variable “t” in the equations of quantum mechanics. The third chapter considers attempts to unify quantum mechanics and general relativity in the late 1960s, which prompted physicists to question iii the “existence” of time in relation to the universe as a whole. In each episode considered, physicists engaged with the concept of time in a variety of ways, revealing a multiplicity of relationships between physics, philosophy, and time. Further, in each case physicists brought a unique set of assumptions to their concepts of time, revealing the variety ways in which fundamental concepts functioned and changed in late twentieth century physics. The result is a heterogeneous picture of the practice of physics, as well as one of physics’ most basic concepts. iv TABLE OF CONTENTS Acknowledgments vi INTRODUCTION 1 CHAPTER ONE Atomic Times: Clocks and Time Standards in the Post-War era 34 CHAPTER TWO The Discovery of CP Violation: Physics, Fundamentality, and the Arrow of Time 76 CHAPTER THREE Time and Quantum Gravity: Wheeler, DeWitt, And the “Equation of the Universe” 120 CONCLUSION 177 v ACKNOWLEDGEMENTS This project would not have been possible without the tremendous help and support I received along the way. I would like to thank the archivists and librarians who have assisted me from the following institutions: the American Institute of Physics; the American Philosophical Society; the Briscoe Center for American History at the University of Texas, the Harvard University Archives, the M. Louis Salmon Library at the University of Alabama; the National Museum of American History, the National Physical Laboratory Library, the Seeley G. Mudd Manuscript Library at Princeton University, and the US Naval Observatory Library. I would also like to thank the Social Science and Humanities Research Council of Canada, the Charles Warren Center for Studies in American History, the Erwin Hiebert Fellowship for Dissertation Research, and the Harvard Graduate School of Arts and Science for their generous support. I am deeply indebted to Peter Galison, David Kaiser, and Jimena Canales for their insight and guidance throughout the dissertation process. It has been a pleasure working with such an engaged, thoughtful, and encouraging team of advisors. I am also indebted to the wonderful graduate student community at the history of science department at Harvard for their incredible support and encouragement. This project has benefited enormously from their willingness to engage with my ideas in formal and informal contexts. I am particularly grateful for constant support and feedback from Myrna Perez, Stephanie Dick, and Jenna Tonn. Our conversations over brunches, dinners, and glasses of wine have been invaluable to my thinking as well as my overall happiness. vi Special thanks to Myles for his companionship during long days of writing; my grandmother “Bubbie” Joan for nurturing my early interest in science; Rachel, Steph, and Myrna for being the best possible friends; my parents, Valerie, Mauricio, and Glen for the unconditional love and support; and Bryan for absolutely everything. Bryan, this dissertation is dedicated to you. vii INTRODUCTION 1. The concept of time is a central one for contemporary scholars in a range of disciplines, including physics, philosophy, psychology, anthropology, and literary theory. As such, it is a particularly appropriate point of entry for investigating relationships among the disciplines of the late twentieth century. What do conceptions of time, as employed by different groups of scholars, have in in common and how do they differ? How are questions about time framed differently in various disciplines, and which methods are used to answer these questions? What presuppositions about the nature and boundaries of a given discipline contribute to its practitioners’ treatments of time? Even within a traditional academic discipline such as physics, there are subgroups of researchers who understand the concept of time, and the intellectual problems it poses, very differently. Thus, a study of the ways scholars have handled the concept of time can illustrate the relations among disciplines, as well as within a given discipline. This dissertation will examine how different subgroups of physicists, working in the United Sates in the 1950s and 1960s, approached fundamental questions about time. Specifically, it will consider the extent to which each subgroup asked questions about the meaning and nature of time, as well as how speculative and interpretive methods factored into their answers. Within each subgroup, physicists operated under a particular understanding of what it meant to do physics, influencing the types of questions they 1 asked and how freely they speculated about the nature of their central concepts. The primary objective of this dissertation will be to account for the various ways American physicists understood their work and discipline in the decades following World War II, as exemplified by their engagement with the concept of time. This will set the stage for a secondary objective: to understand what a fundamental concept, like time, looks like when situated within shifting understandings of physics. Each chapter focuses on a specific episode in the history of physics in the postwar United States in which the nature of time emerged as a salient issue. The first chapter considers a subgroup of physicists working on the development of atomic clocks and atomic time standards in the 1950s, who engaged in debates over the universality of measures of time. The second chapter considers a subgroup of experimental particle physicists in the early-1960s, whose work raised questions about the directionality of time. The third chapter looks to a subgroup of physicists seeking to unify quantum mechanics and general relativity in the late-1960s, who argued about the existence of time. In each case, leading physicists approached questions about time in remarkably different ways, revealing a variety of relationships among interpretation, physics, and time. The subgroup working on atomic clocks and standards in the 1950s did not overtly acknowledge that their work raised questions about the nature of time, although their definitions of basic timekeeping concepts were in flux. The subgroup of experimental particle physicists in the early 1960s identified questions about the nature of time as at stake in their research, but did not pursue these questions themselves, considering them to be outside the boundaries of their discipline. Finally, the subgroup working on the 2 unification of quantum mechanics and general relativity understood interpretive questions and methods as central to their work. I use the word “subgroup” to refer to clusters of physicists, working directly alongside one another, in pursuit of a related set of problems. Rather than examining “physicists” at the general level, or the large and diverse groups designated by the labels “theorists” and “experimentalists,” I take small groups of physicists, directed toward a specific objective, as my unit of analysis. These subgroups were narrower in scope than professionally designated fields of physics, such as the divisions named by the American Philosophical Society (APS), and did not